The need for a signal light annunciator, loud enough to remind the driver that his signal lights have been left on inadvertently has been addressed in more than one prior patent. However, none have gained wide acceptance. It is believed that this is because the sounds they are designed to emit are unpleasant. One category, characterized by U.S. Pat. No. 4,196,415 delivers a continuous buzz during half of the flashing cycle. Another category, characterized by U.S. Pat. No. 3,343,123 delivers loud, single cycle `click` sounds at the beginning and end of the `on` period. It is believed that these and other prior inventions are too annoying to be considered for purchase and daily use by the average driver.
The invention herein presented, is an improvement over the Troesh invention (No. 3,343,123) in that it connects across the terminals of a standard automotive signal light flasher, uses a capacitor to store charge and uses a noise making device. However, it represents a dramatic improvement because it creates a pleasant, short burst of tone that decays naturally, not unlike a dampened piano key being struck.
This improvement is broght about through the addition of an oscillator circuit that operates at an audio frequency (usually 2 to 4 KHz) which is used to drive the audio transducer. The source of power for the entire circuit, and for the oscillator in particular is the capacitor that charges while the flasher contacts are open, as in the Troesh patent. The size of the capacitor and the resistance in its discharge path in the present invention are chosen so that the capacitor completes its discharge a fraction of a second after the flasher contacts close. This determines the length of the tone and provides the decay as the capacitor looses it's charge. The sound thus created is delivered appropriately only at the beginning of the flasher `on` period, just as the indicator light on the automobile's dashboard is turning on.
A preferred embodiment of the invention uses a piezo-electric disc as the transducer and a modified Hartley circuit as the oscillator. The major improvement this provides is that all of the circuitry, including the capacitor and the oscillator as well as the disc, fit inside the standard plastic cases that are used industry-wide to house piezo-electric buzzers alone. These cases are attractive, are designed to resonate at the frequency of their associated discs, and already incorporate circuit boards. In fact, only these circuit boards would be changed. It is therefore predicted that the cost of this invention to the public would be very modest.
A special interconnector is also presented that improves upon the Troesh interconnector in two important ways. First, though the Troesh interconnector (referred to as a `connecting plate` in the prior patent) does allow the flasher to be connected to both its normal signal light circuit as well as the invention, it does not allow it to occupy its normal location. This is because the interconnector is thick enough to enclose the full length of the standard flasher contacts--approximately one half inch. This creates a problem on automobiles that have covers that are installed over the flashers. The interconnector presented herein overcomes this problem by having sleeve type contacts made of thin metal that slip over the flasher contacts before the flasher is inserted into its normal socket. The sleeve contacts are held in correct orientation prior to use by a thin piece of insulator that remains connected. A pair of wires connect the interconnector to the annunciator itself.
The second improvement is that one of the contacting sleeves of the interconnector is allowed to swivel 180 degrees so that the polarity of the connection to the flasher can be reversed prior to insertion in the flasher socket. This is desirable because the present device has polarized components including the capacitor, the oscillator and the transducer, and because even though the standard flasher contact arrangement is polarized, no standard is followed in the automotive industry on the polarity of the connections to the flasher sockets themselves. This is probably because the flashers alone work equally well either way.